Island Size Research Articles

Understanding the Safety Impact of Protected Intersection Design Elements: A Driving Simulation Approach

Protected intersections are used to facilitate safe crossings for non-motorized users. As a relatively new treatment in North America, it is essential to understand how their design elements, such as bicycle intersection-crossing pavement markings and corner refuge island size, enhance bicyclist safety. A driving simulation experiment was developed to test the effectiveness of different design elements of protected intersections on driver speeds. Participants were exposed to different protected intersection designs that varied with respect to the corner refuge island width and bicycle intersection-crossing pavement marking levels. Their speed at two parts of the right turn, that is, approach and curve speed, was analyzed. A combination of design elements, participant demographics, or bicyclist presence at the intersection affects driver behavior at a protected intersection. The results indicate that the presence of a bicyclist crossing a protected intersection significantly reduces speeds for drivers performing a right turn. Corner refuge islands with larger width were found to reduce speed at the curve as they were accompanied by larger curb extensions which essentially reduce the space for the automobiles. Bicycle intersection-crossing pavement markings influenced only approach speeds prior to the actual turn since that is the location where they were the most visible. Age, gender, and bicycling frequency were observed to affect turning speeds, indicating that design elements alone cannot determine the safety effectiveness of a protected intersection. The findings of this study can guide the implementation of protected intersections.

Raman microscopy and infrared optical properties of SiGe Mie resonators formed on SiO2 via Ge condensation and solid state dewetting

All-dielectric photonics is a rapidly developing field of optics and material science. The main interest at visible and near-infrared frequencies is light management using high-refractive-index Mie-resonant dielectric particles. Most work in this area of research focuses on exploiting Si-based particles. Here, we study monocrystalline Mie-resonant particles made of Ge-rich SiGe alloys with refractive index higher than that of Si. These islands are formed via solid state dewetting of SiGe flat layers by using two different processes: (i) dewetting of monocrystalline SiGe layers (60%–80% Ge content) obtained via Ge condensation of SiGe on silicon on insulator; and (ii) dewetting of a SiGe layer deposited via molecular beam epitaxy on silicon on insulator and ex situ Ge condensation, forming a Ge-rich shell surrounding a SiGe-core. Using high-spatial-resolution Raman microscopy we monitor Ge content x and strain ϵ of flat layers and SiGe-islands. We observe strain relaxation associated with formation of trading dislocations in the SiGe islands compared to the starting SiGe layers, as confirmed by TEM images. For initial high Ge concentration in the flat layers, the corresponding Ge content in the dewetted islands is lower, owing to diffusion of Si atoms from Si or SiO2 into SiGe islands. The Ge content also varies from particle to particle on the same sample. Size and shape of the dewetted particles depend on the fabrication process: thicker initial SiGe layers lead to larger particles. Samples with narrow island size distribution display rather sharp Mie resonances in the 1000–2500 nm spectral range. Larger islands display Mie resonances at longer wavelength. Positions of the resonances are in agreement with the theoretical calculations in the discrete dipole approximation.

Evolution of InAs quantum dots and wetting layer on GaAs (001): Peculiar photoluminescence near onset of quantum dot formation

InAs quantum dots (QDs) have been grown on a GaAs (001) substrate in the subcritical region of InAs coverage for transition from a 2-dimensional (2D) to a 3-dimensional growth mode. Evolution of QDs and the corresponding wetting layer (WL) with InAs coverage has been investigated. Under specific growth conditions, quantum dot formation was observed only in samples where InAs coverage is more than 1.48 ML. The QD density increases sharply with InAs deposition initially but slows down with increased coverage. Photoluminescence (PL) shows the existence of a third peak, other than QD and WL peaks, at the low energy side of the WL peak, which is named the precursor peak. Evidence is presented supporting the theory that this peak is due to 2D InAs islands on a monolayer of InAs, which are small enough to localize excitons. Meanwhile, the WL peak is due to larger InAs islands under high compressive strain. During QD formation, the WL peak energy increases with the increase in InAs deposition. This is due to the sudden transfer of material from the bigger size of InAs islands to the QD. Our results show that the QD, WL, and precursor peaks coexist near the onset of QD formation. The power dependence of the three PL peaks is evident, which supports to our conclusion.

Contrasting Patterns of Movement across Life Stages in an Insular Iguana Population

West Indian rock iguanas (genus Cyclura) represent the most endangered group of lizards in the world, with most taxa restricted to few or single islands. In addition to distribution and availability of resources, factors influencing optimal use of insular space in these large vertebrates may include a combination of social, ontogenetic, and long-term demographic factors. Life stage-specific dispersal and habitat use patterns have previously been characterized in Cyclura, but assessments across the lifespan are lacking. This study evaluates shifting patterns of movement in a single taxon, Cyclura nubila caymanensis. We used mark–recapture and radio tracking simultaneously to assess age- and sex-dependent variation in spatial ecology. Evidence for prolonged site fidelity among adults was consistent with territoriality-modulating space use in this long-lived taxon. Over 5–10 yr, some females were never resighted or recaptured outside of an 80-m perimeter. A notable exception was that gravid females migrated 1.17 ± 0.91 km to utilize coastal areas during the nesting season. In contrast, neonates dispersed farther (2.32 ± 2.26 km) and their trajectories were often nonlinear. Radio-tracked brother–sister pairs exhibited no tendency to disperse together during their first 4 wk, settling into final known locations at pairwise distances of 2.16 ± 1.74 km. Annual net displacement remained high over the first 1–3 yr of life. Our data are consistent with studies of related taxa wherein individual spatial requirements vary with population density and island size. Notably, panmixis of small island iguana populations appears largely driven by pre-reproductive movements.

Vacancy induced robust magnetism in graphene hexagonal-boron nitride in-plane hybrids with hexagonal shaped islands

We present the results of density functional theory (DFT) calculations on the vacancy-defected graphene-hBN (GBN) nanosheet embracing a hexagonal island. Hexagonal shaped h-BN and G islands of varying sizes are respectively patterned in G and h-BN nanosheets for possible uses of GBN hybrid in device applications. Three different types of mono vacancies were formed at various sites of GBN hybrid. Two distinct C mono vacancies, B and N mono vacancy were formed at G/h-BN interface. We additionally formed C mono vacancy in G region, and B and N mono vacancies in h-BN region of the hybrid nanosheet. Possible effects of vacancies and size effects of island on the electronic and magnetic properties of hybrid were examined in great detail. Calculated vacancy formation energies show that N vacancy exhibits lower formation energy than B one. Besides, the interface is the energetically most favorable place, regardless of the type of vacancy. All pristine hybrids with hexagonal islands are non-magnetic semiconductors. However, depending on the type of vacancy and vacancy site, the GBN hybrid can become magnetic with a considerable amount of magnetic moment. Because of the high magnetization energy, the magnetic order is considered to be robust against thermal excitations at finite temperatures. Our results indicated that defective hybrids with G islands have greater potential for magnetic applications. Mono vacancies introduce flat (dispersionless) states near the Fermi level, and these flat energy states lead to localized, integer-valued magnetic moment. In general, no correlation was observed between the island size and the magnetic moment of a defective hybrid. Nevertheless, in the case of C (B) vacancy in G (h-BN) layout, the magnetic moment increases with increasing island size. This result could point to a possible coupling between the defect and hexagonal island.

Challenges and opportunities of zero emission shipping in smart islands: A study of zero emission ferry lines

Abstract Various studies have shown that maritime sector needs increased use of zero emission vessels in service by 2030 in order to achieve an absolute reduction in CO2 emissions of 50% by 2050 (consistent with a 2 °C pathway). These vessels, with operational emissions containing zero or negligible greenhouse gas share, would need to represent a significant portion of newbuilds from that point onwards. The objective of this research is to show the opportunity that implementation of zero emission ferry lines offers in the framework of 100% RES smart island energy systems and demonstrate their ability to supply the fuel for zero emission ferry lines. A method is presented for modelling supply of ferry lines, which are fuelled from excess energy produced by local renewable energy sources. Case study analyses show that operation costs of hydrogen and electric ferry differ depending on the island size and route. Onshore investments are 60% lower in case of electric ferry for short lines, while for longer line onshore investments were up to 4 times higher than the ones needed for the hydrogen ferry line, which had 40% smaller onboard investment costs.

Shapes of Fe nanocrystals encapsulated at the graphite surface

We describe and analyze in detail the shapes of Fe islands encapsulated under the top graphene layers in graphite. Shapes are interrogated using scanning tunneling microscopy. The main outputs of the shape analysis are the slope of the graphene membrane around the perimeter of the island, and the aspect ratio of the central metal cluster. Modeling primarily uses a continuum elasticity (CE) model. As input to the CE model, we use density functional theory to calculate the surface energy of Fe, and the adhesion energies between Fe and graphene or graphite. We use the shaft-loaded blister test (SLBT) model to provide independent stretching and bending strain energies in the graphene membrane. We also introduce a model for the elastic strain in which stretching and bending are treated simultaneously. Measured side slopes agree very well with the CE model, both qualitatively and quantitatively. The fit is optimal for a graphene membrane consisting of 2–3 graphene monolayers, in agreement with experiment. Analysis of contributions to total energy shows that the side slope depends only on the properties of graphene/graphite. This reflects delamination of the graphene membrane from the underlying graphite, caused by upward pressure from the growing metal cluster. This insight leads us to evaluate the delamination geometry in the context of two related, classic models that give analytic results for the slope of a delaminated membrane. One of these, the point-loaded circular blister test model, reasonably predicts the delamination geometry at the edge of an Fe island. The aspect ratio also agrees well with the CE model in the limit of large island size, but not for small islands. Previously, we had speculated that this discrepancy was due to lack of coupling between bending and stretching in the SLBT model, but the new modeling shows that this explanation is not viable.

Island‐biogeographic patterns of spider communities on epiphytes depend on differential space use among functional groups

AbstractAimPositive relationships between island size and species richness have been found for oceanic and non‐oceanic islands. However, the effect of isolation, also predicted by island‐biogeographical theory, seems challenging to test. Species‐specific mechanisms drive the perception of distance and space for animals, and therefore isolation patterns are masked when described at the community level. We used epiphytic plants (canopy islands) and their spider communities to study how functional group and species‐specific use of space modifies the effect of island‐level predictors on species richness.LocationA coffee plantation near Xalapa, Mexico.TaxonSpiders (Araneae), vascular epiphytes (Bromeliaceae, Piperaceae, Orchidaceae, Araceae, Pteridophyta).MethodsWe collected canopy islands from three trees and recorded their three‐dimensional position. Afterwards, we collected all epiphyte‐dwelling spiders. We used Generalized Linear Models (GLMs) to analyse the effect of island size and isolation on the species richness of spider communities and community subgroups (guilds, mobility groups and families). Isolation was calculated using two metrics (aerial and walking distances) associated with different ways of mobility in the canopy (bridging and wandering respectively). We evaluated species‐level associations with island features and tested for sample‐size effects on GLMs using null‐model analysis of ecological networks.ResultsAlthough unimportant at the community level, isolation was more important than island size for some spider subgroups, while having negligible effects for others. Species‐specific responses to isolation and island size were responsible for the variability in species richness patterns observed for broader subgroups (families, guilds and mobility groups). Specific responses of mobility groups to isolation metrics were in line with two ways of moving between islands; one using tree branches as pathways (walking isolation) and the other using silk threads to connect points directly across the air (aerial isolation).Main conclusionsSpatial patterns of epiphyte‐dwelling spiders were explained better when functional traits were considered, and the effect of isolation became apparent only when analysed per functional group, whereas it was masked at the community level. This supports the hypothesis that hunting behaviour and mobility affect the specific perception of space and distance even at the small spatial scale of canopy islands.

Biogeography and anthropogenic impact shape the success of invasive wasps on New Zealand's offshore islands

AbstractAimThe theory of island biogeography predicts that the susceptibility of an island to invasion is determined by its isolation and size. However, many island ecosystems have been intensely modified by humans. Here, we investigated the biogeographic, biotic and anthropogenic drivers of invasive social wasps on 36 offshore islands.LocationIslands off the east coast of New Zealand's North Island.TaxaVespula germanica(Fabricius, 1793),Vespula vulgaris(Linnaeus, 1758) andPolistes chinensis antennalis(Fabricius, 1793), Polistes humilis(Fabricius, 1781).MethodsWe used GIS software for in situ randomization of plots on each island (36 islands, 409 plots) and conducted 5‐min wasp counts to estimate wasp abundance. Wasp abundance and canopy cover were recorded at each plot. Island isolation was measured using GIS software. Data on island size, human settlement and the presence of introduced rats (Rattusspp.) were collated from the literature and island managers. The number of boat docks per island was counted from satellite images. A generalized linear mixed‐effect model (GLMM) was fitted to identify drivers ofVespulaandPolistesabundance on offshore islands.ResultsThe abundance ofVespulawas negatively correlated with island isolation and canopy cover, yet positively correlated with island size.Vespulawere also more abundant on islands that have been settled by humans. The abundance ofPolisteswas negatively correlated with canopy cover. Finally, results did not support the notion that invasive wasps were associated with introduced rats on New Zealand's offshore islands.ConclusionsOur findings highlight the importance of biogeographic factors, such as island size and isolation, for species invasions, and suggest that intact forest cover could contribute to biotic resistance to invasive wasps in island ecosystems. Studies of invasive species should consider the joint effects of biogeographic, biotic and anthropogenic factors to best inform conservation management.

Organization of Squamata (Reptilia) assemblages in Mediterranean archipelagos.

Mediterranean islands have complex reptile assemblages, but little is known about the factors that determine their organization. In this study, the structure of assemblages of Squamata was evaluated based on their species richness and two measures of phylogenetic diversity (variability and clustering). I evaluated the composition of the assemblages comparing distinct biogeographic subregions within the Mediterranean: Adriatic, Aegean, Balearic, Corsica–Sardinia, Crete, Gulf of Gabés, Ionian Sea, Ligurian Sea, Malta, Sicily, and Tyrrhenian Sea. The effect of island environments and geographical isolation on the diversity metrics was assessed using generalized linear models. The analyses indicated that species richness was mostly influenced by island area and geographical isolation. Assemblages on smaller islands were poorer in species and phylogenetically dispersed, possibly as an effect of interspecific competition. The species composition of the assemblages was determined by similar environmental drivers within the biogeographic subregions, including island area, island elevation, geographical isolation, and aridity. In several subregions, significant patterns of phylogenetic attraction were found in species co‐occurrences, caused by the limits imposed by the island size on large predatory species.

Mapping Recent Shoreline Changes Spanning the Lateral Collapse of Anak Krakatau Volcano, Indonesia

We use satellite imagery to investigate the shoreline changes associated with volcanic activity in 2018–2019 at Anak Krakatau, Indonesia, spanning a major lateral collapse and period of regrowth through explosive activity. The shoreline changes have been analyzed and validated through the adaptation of an existing methodology based on Sentinel-2 multispectral imagery and developed on Google Earth Engine. This work tests the results of this method in a highly dynamic volcanic environment and validates them with manually digitized shorelines. The analysis shows that the size of the Anak Krakatau Island increased from 2.84 km2 to 3.19 km2 during 15 May 2018–1 November 2019 despite the loss of area in the 22 December 2018 lateral collapse. The lateral collapse reduced the island area to ~1.5 km2 but this was followed by a rapid increase in area in the first two months of 2019, reaching up to 3.27 km2. This was followed by a period of little change as volcanic activity declined and then by a net decrease from May 2019 to 1 November 2019 that resulted from erosion on the SW side of the island. This history of post-collapse eruptive regrowth and coastal erosion derived from the shoreline changes illuminates the potential for satellite-based automated shoreline mapping to provide databases for monitoring remote island volcanoes.

Measuring the transition between nonhyperbolic and hyperbolic regimes in open Hamiltonian systems

We show that the presence of KAM islands in nonhyperbolic chaotic scattering has deep implications on the unpredictability of open Hamiltonian systems. When the energy of the system increases, the particles escape faster. For this reason, the boundary of the exit basins becomes thinner and less fractal. Hence, we could expect a monotonous decrease in the unpredictability as well as in the fractal dimension. However, within the nonhyperbolic regime, fluctuations in the basin entropy have been uncovered. The reason is that when increasing the energy, both the size and geometry of the KAM islands undergo abrupt changes. These fluctuations do not appear within the hyperbolic regime. Hence, the fluctuations in the basin entropy allow us to ascertain the hyperbolic or nonhyperbolic nature of a system. In this manuscript, we have used continuous and discrete open Hamiltonian systems in order to show the relevant role of the KAM islands on the unpredictability of the exit basins, and the utility of the basin entropy to analyze this kind of systems.

A Nationwide Survey of Obstetric Care Status on Japan's Islands, with Special Reference to Maternal Transport to the Mainland.

Safe obstetric care is a worldwide requirement. In Japan, a reduced number of obstetricians has prompted the centralization of obstetric facilities, and Japan's islands are expected to experience problems in handling deliveries. Although many pregnant women "move" to the mainland at later gestational weeks, "transport" from the island to the mainland may be occasionally needed when disorders manifest before the "move." Other women plan within-island deliveries; however, transport is required when complications arise. Managing delivery- or pregnancy-related problems may differ in transport by the population size of islands. We investigated the following issues in relation to the population size of Japan's islands: 1) How were deliveries handled on islands? 2) How many pregnant women were transported to the mainland? 3) What was the reason for and what affected transport? A total of 142 municipalities were selected to participate in a questionnaire survey, and 108 institutions from 106 municipalities responded. A comparative analysis by island size was performed using 2014 data: small-sized (population < 1,000), mid-sized (1,000 to 5,000), and large-sized (≥ 5,000). The percentage of women transported to the mainland from small-sized islands was significantly higher than that from large-sized islands (6.8 vs. 2.6% of all births in a year, respectively, P < 0.01). Transport was mainly in response to threatened preterm labor. Adverse weather was the most frequent factor affecting transport reliability. Our findings may contribute to a more detailed understanding of the state of obstetric care on Japan's islands.

On the surface integrity of additive manufactured and post-processed AlSi10Mg parts

The research centres on the evaluation of surface integrity of AlSi10Mg parts produced via laser-based powder bed fusion (LPBF) process, followed by vibratory surface finishing. The alloy is chosen for its applications in lightweight components used in electronic packaging, automotive and aerospace sectors. Initial experiments involve optimisation of key LPBF process parameters by analysing the surface roughness and density data of the built parts. A Taguchi L18 orthogonal array is used for the optmisation trials with variations in the laser power (P), beam scanning speed (v), hatch spacing (H) and island size (I). Latter experimental phase deals with microhardness and microstructure assessment of heat treated LPBF specimens that are produced using the optimised LPBF parameters, i.e. P: 250 W, v: 1500 mm/s, H: 75 µm and I: 2 mm. Microhardnesses of the annealed samples reduce by ~12% with respect to the as-built parts and the values remain almost unchanged from the annealed state following solution treatment and ageing. The fish-scale like melt-pools observed on the unheat treated samples begin to fade off in the annealed specimens and completely disappear after solution treatment and ageing, with silicon particles dispersed all over the aluminium matrix. The final experimental phase involves vibratory surface finishing of the as-built LPBF parts using a vibrating ceramic media mixed with different acid and amine based liquid compounds for 1-6 hours, followed by vibrating in a maize based media for another 1-6 hours. The process aids in reducing the parts’ roughness, Sa by ~35-70%, however the effect is more prominent when using the ceramic media.

Observation of Coulomb Gap and Enhanced Superconducting Gap in Nano-Sized Pb Islands Grown on SrTiO3**Supported by the National Natural Science Foundation under Grant Nos. 11674191 and 11825404, the National Key Program for S&T Research and Development under Grant No. 2016YFA0301002, and the Beijing Advanced Innovation Center for Future Chip (ICFC). W.L. was also supported by Beijing Young Talents Plan.

We report high-resolution scanning tunneling microscopy (STM) study of nano-sized Pb islands grown on SrTiO3, where three distinct types of gaps with different energy scales are revealed. At low temperature, we find that the superconducting gap (Δs) in nano-sized Pb islands is significantly enhanced from the one in bulk Pb, while there is no essential change in superconducting transition temperature Tc, giving rise to a larger BCS ratio 2Δs/kBTc ∼ 8.31 and implying stronger electron-phonon coupling. The stronger coupling can originate from the interface electron-phonon interactions between Pb islands and SrTiO3. As the superconducting gap is totally suppressed under applied magnetic field, the Coulomb gap with apparent V-shape emerges. Moreover, the size of Coulomb gap (ΔC) depends on the lateral size of Pb islands (R) with ΔC ∼ 1/R0.35, indicating that quantum size effect can significantly influence electronic correlations. Our experimental results shall shed important light on the interplay among superconductivity, quantum size effect and correlations in nano-sized strong-coupling superconductors.

International linkages, geopolitics, and the Belt and Road Initiative: A comparison of four island territories

Existing literature has placed a strong emphasis on foreign linkages for the sustainability of island territories. However, studies have largely focused the effect of Western linkages, leaving the rise of Asian linkages unexplored. Such an investigation is of increasing significance given China’s rise in global politics and its ambitious Belt and Road Initiative (BRI). This article explains island territories’ inclination towards this newfound Chinese influence by comparing two Danish island territories and two Chinese island territories and argues that island territories with strong international linkages tend to face more challenges to accept the BRI, as demonstrated by the cases of Greenland and Hong Kong with stronger US strategic, military, and diplomatic linkages; and vice versa for the Faroe Islands and Macau with relatively weak international linkages. This paper contributes to the literature by moving beyond internal factors, including island types, sizes, and peripheralities, to explore how external factors, namely foreign linkages in international politics, from an alternative geopolitical perspective.

Structure of Island Gold Films on Thermobarically Sintered Cubic Boron Nitride

The structure of island gold films on the surface of cubic boron nitride is reported. The average size of islands, the nature of their distribution on the surface, and the average number per surface unit are given.

Исследование поглощения СВЧ излучения в сверхтонких проводящих пленках

An interaction numerical simulation of the microwave range electromagnetic waves with nanometer thickness conductive films, which are approximated by homogeneous region and micro- or nanoparticle’s structures, is carried out. Using the rigorous coupled wave analysis, the optical coefficients change dynamics is studied from values characterize dielectric to values for uniform conductive films, and the influence of conductive islands size and distribution on the electromagnetic characteristics is analyzed.

Arctic River Delta Morphologic Variability and Implications for Riverine Fluxes to the Coast

AbstractArctic riverine fluxes are anticipated to increase as the Arctic warms and have a large impact on the Arctic ocean. Deltas modify the spatial and temporal distributions of riverine fluxes, but no thorough studies have been conducted to analyze Arctic delta morphologies to determine their influence on land‐ocean fluxes. We performed an analysis of six high‐latitude deltas (Colville, Kolyma, Lena, Mackenzie, Yenisei, and Yukon) to characterize delta morphologies and determine the influence of morphology on the distribution of fluxes to the coast. All six deltas deliver material to the coast at discrete locations across small areas despite differences in delta shoreline length. Large Arctic deltas exhibit large variability in channel width, which we hypothesize is due to a feedback with ice cover and retreat that favors the growth of large channels over geologic timescales. Spatial variability in island sizes suggests variability in channel activity, island nourishment, and susceptibility to drowning by sea level rise. Potential lake storage is highest on the Mackenzie delta, thus providing a means for reducing nutrient and sediment loading of the coastal ocean. Connected lakes are also prevalent on the Colville and Yukon deltas, suggesting that these deltas can filter riverine fluxes even when the deltas are not flooded. Differences in Arctic delta morphologies can be explained by varying levels of riverine and marine influence, antecedent topography, and local channel dynamics. Ice cover also plays a large role in controlling Arctic delta morphologies and dynamics that has not been previously represented in interpretations of existing delta metrics.

Direct and indirect effects of island size and wave exposure on shoreline arthropod diversity

AbstractAimAvailable theories suggest that the species number increases with island size, but the relationship between island size and species density, the number of species per unit area, is less understood. Moreover, mechanisms connecting island size and species density are not always evident because small and large islands differ in physical characteristics other than island size. The purpose here was to disentangle direct and indirect effects of island size and wave exposure on the species density of arthropods from herb‐dominated shore habitats.LocationIslands in the Stockholm Archipelago, Sweden.TaxonSpiders (Araneae) and beetles (Coleoptera).MethodsWe collected spiders and beetles on vegetated shores on islands of varying sizes, and used structural equation models to disentangle direct and indirect island size and wave exposure effects on species density.ResultsIsland size affected diversity of web‐building spiders, predatory beetles and other beetles (detritivores and omnivores), direct and indirectly. Indirect effects arose because large islands have more trees and steeper slopes than small islands, both of which affected species occurrence. Because height above the sea level reduces the effect of wave exposure, there were effects of these variables on the forest cover and on the diversity of web‐building spiders. Finally, surrounding forest cover and diversity of flowering plants within sites increased diversity of herbivore beetles and cursorial spiders, likely because these sites provide more diverse resources.Main conclusionsThe result that predictors for species density vary between functional groups, with mechanisms that may or may not relate to island size, suggest potential developments in island biogeography theories. Future studies of island size effects should also attempt to quantify indirect effects, and not only total effects.